1. Field of the Invention
This invention relates generally to hard contact lens storage cases, and more particularly to hard contact lens storage cases having suction cups for holding so called hard contact lenses while they are suspended in soaking solutions contained in the storage cases.
2. Description of the Prior Art
Storage cases having suction cups for holding hard contact lenses while they are suspended in soaking solutions are well known. Representative patents disclosing such suction cups would include U.S. Pat. No. 4,167,283; British Pat. No. 1,197,161 and West German Pat. No. 2,301,538. As seen in FIG. 6 of U.S. Pat. No. 4,332,318 suction cups of this type are very often attached to stems which are in turn attached to the underside of the cap of the vial which contains the soaking solution. These patent drawings often depict their suction cups as having distinct rims which are as wide as the walls of the suction cups are thick. See for example FIG. 2 of U.S. Pat. No. 4,167,283 and FIG. 6 of U.S. Pat. No. 4,332,318. However, these depictions are more the result of the patent draftman's attempts to show the body of the suction cup and their associated stems than the physical reality of these suction cups when they are closely observed. In point of fact, the rims of these suction cups are not as wide as the thickness of the sides of the suction cups; they are much more narrow because of the way in which they are manufactured. These cups are produced by the cooperative action of two molds. The first mold has a hollow core which is shaped like a stem with a pod at one end. The pod forms the body of the suction cup. The concave upper surface of the suction cup is formed by the second mold. This second mold is a cylindrical molding pin having a convex head on one end which protrudes into the pod of the first mold. The cylindrical molding pin is inserted into a round molding chamber much like the way a bullet is inserted into the firing chamber of a rifle. The cylindrical molding pin is analogous to the shell case and the convex head is analogous to the bullet's head. In the case of the prior art molding pins, however, there are no discontinuities where the convex head and the cylindrical body come together. In other words, the diameter of the prior art convex head at its base is equal to the diameter of the cylindrical body of the molding pin. The equality of these two dimensions is important for reasons which can now be elaborated upon in terms of the methods by which the suction cups are produced. We should first not that the convex head of the second mold is inserted into the pod of the first mold so that only a thin gap exists between the concave pod and the convex head which protrudes into the pod. The plastic forming material is injected into the first mold up to and including the gap between the pod forming first mold and the convex head of the second mold. The material from which the suction cup is made is then plasticized. These materials are often referred to in this art as "elastomers" and a common example is known by the trade name Kraton. In any event the setting up of these materials results in the formation of a concave suction cup which, then, along with its associated stem, is withdrawn from the mold. The rims of the suction cups formed by this method, when viewed in a cross sectional view, appear as a point or at best a very narrow ledge depending on the degree of magnification. To the naked eye, a ledge is not discernible at the rim of the suction cup. Rather a cross section of the rim of the suction cup appears to come to a point. Furthermore, when viewed from the side under about 10 to 1 magnification these prior art rims do not appear as a straight line but rather as a very jagged edge. This jagged edge results when the plasticized material forming the pinched in rim edge is withdrawn from contact with the second mold. Since the pinched rim has relatively little body compared to the sides of the suction cup, the edge tends to tear as the suction cup is withdrawn from such molds. Unfortunately, these jagged edges permit air leaks between the suction cups and the hard contact lenses they are supposed to hold. Typically, suction cups made with such molds will not hold their suction for more than a few hours. Hence, the user often finds his hard contact lenses at the bottom of the storage vial for the soaking solution. Any number of different courses of action for retrieving the lenses from the bottom of the case are tedious, time consuming, injurious to the lenses and usually serve to contaminate the soaking solution. Therefore, suction cups with the ability to hold hard or semi-rigid, gas permeable contact lenses in place for periods of from 8 to 12 hours, e.g., overnight, would eliminate many of the above noted bad consequences which result from loss of the suction force between the hard contact lenses and the concave bowl of the suction cup. For the purposes of this disclosure, the term "hard contact lenses" should also be taken to include semi-rigid, gas permeable lenses which are usually comprised of about 40% silafocon A and about 60% polymethylmethacrylate.
Regardless of whether the lenses are of the hard or the semi-rigid, gas permeable type, the problems associated with storing these lenses in soaking solutions by means of suction cups can be greatly reduced by modifying the configuration of the convex head of the molding pin used to form the concave bowl of the suction cup. Rather than having the diameter of the base of the convex head equal to the diameter of the cylindrical body so that there is a smooth contour between the head of the convex head and the outside surface of the body of the cylinder, the diameter of the convex head is purposely made smaller than the diameter of the cylinder. This, in effect, creates a ledge between the base of the convex head and the outside surface of the body of the cylinder. The existence of this ledge allows the plastic material to form a suction cup rim which when viewed in cross section, is relatively wide rather than pinched to a point. The wide ledge and the added "body" or volume of the ledge, vis-a-vis the pinched in rims found in the prior art, produces a lens contacting surface which, when viewed from the side, has a smooth edge rather than a jagged one.
Preferably, the width of the ledge, as seen by a side cross sectional view of the pin, will be from about 1 to about 20 percent of the diameter of the cylindrical body of the molding pin. Most preferably the width of the ledge will be from about 2 to about 10 percent of the cylinder diameter. The ledge, when viewed by holding the cylinder's long axis in a vertical plane, can deviate somewhat from a horizontal plane. A downward sloping ledge is however preferable to an upward sloping ledge since an upward sloping ledge tends to create a more narrow ledge surface which if carried to the extreme creates the same pinched rim problems encountered with the prior art suction cups. However, for reasons associated with the machining of the ledge on the end of the molding pin, as well as for reasons of getting good lens/ledge contact, a horizontal ledge is highly preferred. Likewise, for machining reasons, the convex head is preferably a dome which appears from its side cross sectional view to vary from a semicircle (i.e., the radius at the height of the dome is half the diameter of the dome at its base) to a truncated dome wherein the height of the dome is less than the base diameter of the dome.